The present invention relates to a control circuit and more specifically to a control circuit for a cool/heat pump room air conditioner.
Room air conditioners are well known and are of the type that generally fit in a window or in a sleeved opening formed through the wall of a room. Most such room air conditioners utilize a fluid refrigerant which is caused to alternately expand and condense to provide the desired cooling effect inside the room and to expel heat outside of the room. The refrigerant flows through a system which includes an evaporator where liquid refrigerant is permitted to evaporate thereby cooling a coil surface of the evaporator in order to extract heat from air within the room. A fan is used to cause room air to flow over the coil of the evaporator. The refrigerant then flows to the compressor where it is returned to a high pressure gas state. The refrigerant then flows to a condenser, generally positioned outside of the room wherein the refrigerant vapor condenses and gives off heat. Generally a fan is also provided on the condenser side to provide a flow of outside air over the condenser coil to remove heat therefrom. Refrigerant then flows to an expansion device where it is turned to a low pressure liquid state before flowing again to the evaporator.
It is known that by reversing the flow through the system, the air conditioner can act as a heat pump to draw heat from exterior of the room and to provide that heat to the interior of the room. In such an arrangement the refrigerant flow is reversed and what was the evaporator now acts as the condenser to release heat and what was the condenser now acts as the evaporator to absorb heat from the surrounding air.
Control systems for room air conditioners are well known and in such control circuits generally include a switch for powering a compressor motor and a fan motor as well as sometimes controlling other components.
Generally the type of motors utilized in such air conditioners have both a main winding and an auxiliary winding with capacitors in series with the auxiliary winding. Control circuits which have been provided for such air conditioning units and motors are disclosed in the following U.S. Pat. Nos. 2,242,370; 2,782,351; 3,045,159; 3,146,387; 3,385,077; and 3,852,648. Such circuits are limited to air conditioner units, however, and do not appear to provide the necessary controls for heat pump operation.
The above listed patents describe various types of control circuits and including circuits in which a single, dual rated capacitor is used in series with each of the two motor auxiliary windings.
In applications where a room air conditioner is also being utilized as a heat pump to provide indoor heating, additional considerations arrived over those necessary for controlling a room air conditioner, that is, the need to be assured that the evaporator does not develop an exterior coating of ice since this severely deteriorates the efficiency of the device.
In order to avoid a separate de-icing circuit for periodically de-icing the evaporator coil, the device embodying the present invention utilizes a separate electric heater which is utilized when the outdoor temperature is such that the outdoor heat exchanger is about to frost over.
Since it is still necessary for the fan motor to operate when the electric heater is operating, but when the motor driven compressor is not operating, it is necessary to sometimes operate the one motor at full power while the other motor is off.